Anchor

ABSTRACT

An anchor comprising flukes, a shank hinged to the flukes and transversely extending stabilizing arms, wherein the hinge point of the shank substantially coincides with the geometric centre of the fluke surface area and head faces are provided on either side of the hinge point, which head faces are formed by head plates spaced from the geometric centre of the fluke surface area, which head plates converge towards the front of the flukes both in vertical and in horizontal direction, delimit the slewing angle of the shank and are connected to the flukes by means of support plates parallel to the shank. The hollow flukes are joined behind the hinge point of the shank to form one fluke surface and converge towards their sharp front, side and rear edges along flowing lines.

United. States Patent 1191 van den Haak [4 1 Sept. 2, 1975 ANCHOR [76]Inventor: Rob van den Haak, Codijn van Dormaalstraat 150, Rotterdam,Netherlands 22 Filed: July 11, 1974 21 Appl. No.: 487,538

abandoned.

[30] Foreign Application Priority Data Apr. 10, 1972 Netherlands 7204763[52] US. Cl 114/208 R [51] Int. Cl B63b 21/38 [58] Field of Search114/207, 206 R, 208 R,

[56] References Cited UNITED STATES PATENTS 2,282,566 5/1942 Danforth114/208 R 2,641,215 6/1953 Danforth... 114/208 R 2,743,695 5/1956Bowman... 114/207 2,981,219 4/1961 Wins1ow.... 114/208 R 3,274,9699/1966 Boas 114/208 R 3,306,248 1/1967 Austin 114/208 R 3,373,712 3/1968Stokes 114/208 R 3,822,664 7/1974 Hedman 114/208 R FOREIGN PATENTS ORAPPLICATIONS 143,111 12/1950 Sweden 114/208 R 809,949 4/1969 Canada114/208 R Primary Examiner-Trygve M. lBlix Assistant Examiner-Sherman D.Basinger Attorney, Agent, or Firm-Marn & Jangarathis [57] ABSTRACT Ananchor comprising flukes, a shank hinged to the flukes and transverselyextending stabilizing arms, wherein the hinge point of the shanksubstantially coincides with the geometric centre of the fluke surfacearea and head faces are provided on either side of the hinge point,which head faces: are formed by head plates spaced from the geometriccentre of the fluke surface area, which head plates converge towards thefront of the flukes both in vertical and in horizontal direction,delimit the slewing angle of the shank and are connected to the flukesby means of support plates parallel to the shank. The hollow flukes arejoined behind the hinge point of the shank to form one fluke surface andconverge towards their sharp front, side and rear edges along flowinglines.

7 Claims, 1 Drawing Figure ANCHOR This is a continuation of applicationSer. No. 348,164, filed Apr. 5, 1973, and now abandoned.

The invention relates to an anchor comprising at least two flukes, ashank hinged to the flukes and transversely extending stabilizing arms.

In addition to the long-known stock anchors and more recent stocklessanchors, during the last 30 years many new types of anchors have beentested and adopted for use. The best-known new types are the US. Navytype LWT anchor, the Pool anchor, the Danforth anchor, the Stato anchorand the Delta anchor. Except for the Delta anchor, which has a flukewith a fixed shank, these anchors comprise shanks hinged between therear ends of the flukes. To avoid tilting of the anchor, the LWT anchor,the Danforth anchor and the State anchor comprise a stock mounted in theflukes in or near the hinge point of the shank transverse to thedirection of pull.

Due to the improved anchor types, the anchorage ground has come to playa more important part than this was hitherto the case with theold-fashioned stock anchors. Present day anchors will less easily burythemselves in weak ground. However, the shoulders will find less grip onhard ground, so that the flukes need more time to dig in.

Good anchorage grounds are, for example: normal sea clay, hard sand andsoft lime.

Bad anchorage ground is, for example: gravel (i.e. fine pebbles withcoarse sand).

Extremely bad anchorage grounds are:

coarse pebbles with hard clay and rock;

shells with hard clay;

soft sand on a rocky bottom.

Mud constitutes good anchorage ground for the oldfashioned anchors andheavy conventional types, whereas it constitutes definitely badanchorage ground for the modern types, such as the Danforth anchor.

Clay and soft lime tend to stick to the flukes of the Danforth anchor,thereby forming a lump of material which obstructs and even preventsdigging-in of the flukes after the anchor has broken out or has beentoppled over due to swaying of the ship.

The behavior of different types of self-burying anchors 1. In the caseof a certain type of anchor the maximal holding power is achieved onlyat a specific fluke angle (the angle between the fluke surface and theshaft).

2. Long flukes produce great resistance against toppling over of theanchor due to swaying of the ship, which often results in bent anchorshanks (Danforth and LWT anchor).

3. Vertical stiffenings on the inside of the flukes compress the ground,as a result whereof the anchor will form a lump and break out (Danforthand LWT anchor).

4. The holding power increases as the anchor buries itself deeper in theground.

5. Preferably, in front view an anchor should have an optimally smallsurface area so as to be able to dig in easily.

6. Shoulders disposed transversely to the flukes highly reduce theburying capacity.

7. Usually, the rear end of an anchor is provided with a head serving todispose the fluke in a downwardly slanting position when the anchorrests on the sea bottom, which is particularly important in hard ground,where there is a greater chance that the front of the fluke will not digin but will drag over the ground (socalled scratching).

8. Short shanks, short stocks and large fluke angles each individuallyand, to a greater extent, in combination promote lifting of the headwhen a pulling force is applied to the anchor, which causes the anchorto tilt so that one side of the fluke will be dragged over the ground.

9. Anchors the stock and flukes of which have a fixed position relativeto each other (e.g. the Delta anchor) are possible, privided it isensured that the stock and the shank are long enough and the fluke angleis small. When the anchor is placed on the end of the stock, the end ofthe shank and the tip of the fluke, it should automatically assume theproper burying position.

10. Anchors the fluke tips of which are wide apart are liable to rotate,as when the anchoris dropped on the bottom in a slanting position and,consequently, one fluke is lower than the other, the lower fluke willbury itself deeper than the other fluke and the resultant torque resultsin rotation and breaking out of the anchor.

The breaking out of anchors consequently, only a The break-out forcedepends upon the anchorage ground, duration of the anchorage period and,particularly, the holding power required. An anchor whereto only aslight pulling force has been applied will have hardly buried itselfand, consequently, only slight break-out force is required for liftingthe anchor. However, when the anchor had to supply the maximal holdingpower, it will have buried itself deeply to produce this holding powerand it will be self-evident that a large break-out force is required forlifting the anchor.

Practical experiments show that when a catting eye is provided at thefoot of the head of the anchor for lifting purposes, the breakout forceis 40% and more of the available holding power. This applies topractically any type of anchor. However, when the catting eye isprovided at the upper end of the shank, the break-out force will beconsiderably reduced as the shank will function as a proper lever.

The break-out force is proportional to the length of the flukes beforethe hinge point of the shank, i.e., the longer the flukes the higher therequired break-out force.

It is an object of the invention to provide an anchor having highself-burying capacity in any kind of anchorage ground, a high stability,i.e. resistance to lateral turning and, consequently, dragging of theanchor, a high holding power but a low break-out force.

To this end the anchor in accordance with the invention is formed suchthat the hinge point of the shank substantially coincides with thegeometric centre of the fluke surface area with head faces beingprovided on either side of the hinge point.

In accordance with the invention the head faces may be formed by platesspaced from the fluke surface and connected to the flukes by means ofsupport plates parallel to the shank. In accordance with a preferredembodiment of the invention the head plates are provided such that theyconverge towards the front of the flukes. Furthermore, in accordancewith the invention the head plates may be provided such that theydelimit the slewing angle of the shank. Furthermore, in accordance withthe invention the head plates may have the form of an isoscelestrapezium converging towards the front. The head plates have such awidth that, when the anchor is dropped on the anchor chain with theshank in the wrong direction, the anchor will rotate about its centre ofgravity without tilting when the anchor chain is pulled. When the anchorchain is caught between the fluke and the shank, upon pulling the fluketips will be raised so that the chain is released. This is contrary toanchors having head plates mounted at the back, as in these cases theweight distribution of the flukes is such that it is practicallyimpossible to tilt the fluke tips over the chain.

In order to obtain a rigid structure, in a preferred embodiment of theinvention the flukes are joined behind the hinge point of the shank toform one fluke surface.

For considerations of rigidity and reduction of weight of the anchor, inaccordance with the invention the flukes are hollow and converge alongflowing lines towards their sharp front, side and rear edges.

Instead of the stock present in most anchors, the anchor in accordancewith the invention comprises stabilizing pins provided on either side ofthe flukes at about one-third of the fluke length from the rear edge.This is contrary to conventional anchors having the stockes mounted atthe rear edge of the flukes. These stabilizing pins are directedslightly backwardly to easily pass obstacles that may be prevent on thebottom. The new anchor has sharp, smooth flukes to obtain good dig-inand burying properties.

The head plates, the shape and position of which provide minimalresistance to burying, automatically place the flukes in the properdig-in position.

In a thin layer of sand on a hard subsoil the short fluke length beforethe hinge point of the anchor and the fluke portion therebehind providea (to 50%) higher holding power than, for example, a Danforth anchor ofthe same weight but having a far longer fluke length before the hingepoint of the shank.

The large surface area behind the hinge point will grip the moved groundfor a larger period of time, which results in a large holding power. Dueto the short fluke length before the shank, this shank may be farshorter than that of the Danforth anchor or other known anchors,provides an important weight reduction.

Although the burying capacity is very large, the break-out force isrelatively slight as the catting eye is built-in in the rear side of onefluke (about 24% of the holding power). The breaking-out of the anchorover the head also requires relatively slight force (about 13% of theholding power) as the fluke portion before the hinge point of the shankis relatively short and the fluke portion behind the hinge point acts asa lever, while, moreover, the fluke rotates about the lower head plate.

Comparative anchor tests have been performed by the Dutch Department ofWays and Waterworks in March 1973 in the Oosterschelde. These testsshowed that in tidal stream, in firmly compacted sand and at about 4.5 mdepth, a so-called Stevin anchor in accordance with the invention havinga weight of 950 kg can supply a maximal holding power of 32 tons, i.e, aholding power efficiency of 33.6. A Danforth anchor of 900 kg tested atthe same location under identical conditions supplied a maximal holdingpower of 13.2 tons, i.e., a holding power efficiency of 14.7.Consequently, the holding power of the Stevin anchor is 2.29 times aslarge as that of the Danforth anchor.

The invention will be elucidated hereinafter with reference to thedrawing showing and embodiment of the anchor.

In the drawing the anchor comprises two relatively thick flukes 1 and 2separated by a slot 3, the surfaces of the flukes sharply convergingtowards the outer edges. At 4 the rear edges of the flukes are joined toform one fluke surface. The relatively large flukes are hollow to reducethe weight of the anchor. A shank 6 disposed in the slot 3 is hinged tothe flukes 1 and 2 in the geometric centre 5 of the common fluke surfacearea.

Between the shank 6 and the parallel vertical inner faces 7 and 8 of theflukes l and 2 two support plates 9 and 10 are secured to the flukesnormal to the fluke surface, which support plates extend above and belowthe flukes.

Isosceles trapezoidal head plates 11 and 12 are welded to the supportplates behind the geometric centre 5 on either side of the flukes, thesides of the trapezium converging towards the shank 6. The supportplates are formed such that the headplates l1 and 12 converge towardsthe front of the anchor flukes and are preferably directed to the tipsof the flukes.

With their bevelled front edges 13 and 14, respectively, the head platesdelimit the slewing angle of the shank relative to the flukes andfurther serve to dispose the flukes at the correct angle relative to thesea bottom as soon as the anchor hits the bottom, so that the flukes caneasily dig in.

As the head plates are only at a small angle relative to the plane ofthe flukes, their resistance to digging-in only slightly affects theburying properties of the anchor, whereto the sharp fluke edgescontribute in a favourable manner.

Instead of the stock present in most anchors, the anchor in accordancewith the invention comprises stabilizing pins 15 and 16 provided oneither side of the flukes at about one-third of the fluke length fromthe rear edge, which stabilizing pins may be hollow to reduce the weightand may be directed slightly backwardly relative to the transverselydirected hinge axis. In this manner cables or hawsers present on the seabottom will easily slip off the stabilizing pins.

I claim:

1. An anchor comprising:

an anchor base comprised of upper wall means, lower wall means spacedapart from said upper wall means and inner wall means defining anenclosure within said wall means, said upper and lower wall meansconverging towards each other to form sharp leading and side edges, saidinner wall means extending from said leading edge to a pointintermediate said leading edge and a trailing portion of said anchorbase thereby forming fluke means,

a shank means hingedly mounted between said fluke means at a pointsubstantially coincident with the geometric center of said anchor base;and

head face means mounted to said anchor base about either side of saidpoint.

2. The anchor as defined in claim 1 wherein said head face meansincludes head plate means spaced apart from said front and back wallmeans, said head plate means converging towards the leading edge of saidfluke means and extending forward and rearward of said point.

the length of said fluke means.

6. The anchor as defined in claim 1 wherein said fluke means include alarge surface area on a side of the anchor base opposite to said shankmeans.

7. The anchor as defined in claim 1 wherein said trailing portion ofsaid anchor base is a sharp rear edge formed by said upper and lowerwall means converging towards each other at the trailing edges thereof.

1. An anchor comprising: an anchor base comprised of upper wall means,lower wall means spaced apart from said upper wall means and inner wallmeans defining an enclosure within said wall means, said upper and lowerwall means converging towards each other to form sharp leading and sideedges, said inner wall means extending from said leading edge to a pointintermediate said leading edge and a trailing portion of said anchorbase thereby forming fluke means, a shank means hingedly mounted betweensaid fluke means at a point substantially coincident with the geometriccenter of said anchor base; and head face means mounted to said anchorbase about either side of said point.
 2. The anchor as defined in claim1 wherein said head face means includes head plate means spaced apartfrom said front and back wall means, said head plate means convergingtowards the leading edge of said fluke means and extending forward andrearward of said point.
 3. The anchor as defined in claim 2 wherein saidface means are in the form of isosceles trapeziums.
 4. The anchor asdefined in claim 1 wherein said plate means are mounted on support platemeans affixed to said anchor base means and parallel to said shankmeans.
 5. The anchor as defined in claim 1 and additionally comprisingstabilizing pin means positioned on said side edges of said anchor baseat a point from said trailing portion of said anchor base of aboutone-third of the length of said fluke means.
 6. The anchor as defined inclaim 1 wherein said fluke means include a large surface area on a sideof the anchor base opposite to said shank means.
 7. The anchor asdefined in claim 1 wherein said trailing portion of said anchor base isa sharp rear edge formed by said upper and lower wall means convergingtowards each other at the trailing edges thereof.